1. Field of Invention
This invention is related to an pipelined buffer driving an output voltage to be equal to the voltage of an input analog signal.
2. Description of Prior Art
The analog buffer is to drive the output voltage to be equal to the voltage of an input analog signal. In the prior arts, the analog buffer is a unit gain amplifier. In unit gain amplifier, the output is connected to be one of the inputs of a differential amplifier. In such a circuit configuration, the output load has a direct impact on the input. It takes a long time to be stable. Even worse, the weak input analog signal is destroyed. Furthermore, the output stage of amplifier is constituted of large devices. It consumes a lot of dc bias current. Such a large power consumption is not acceptable for very large scale integration.
I make the innovative design to overcome these problems by decoupling the long global feedback loop to be several local feedback loops. Furthermore, in the high gain amplifier, each feedback loop is constituted of only one MOS gate. To have both accuracy and speed, the key design is the voltage clamping circuit. According to the analog input signal, two clamping voltages are generated with a level shift circuit. The clamping voltages then clamps the output voltage dynamically. If the output voltage is equal to the input voltage, the large output devices are switched off to save power. With the local feedback loops and the voltage clamping circuit, the analog signal can propagate in the pipelined analog buffer. It increases the signal bandwidth and the output load has no impact on the input signal. So far, none of the references has the superior features of this analog buffer.
The pipelined analog buffer has an important application of power supply. One example is the voltage source for the TTL compatible input buffer. The trigger point of the TTL input buffer is about 1.4 volts; the voltage source is about 2.8 volts. The prior arts used the unit gain amplifier to generate the 2.8 volt, such as the U.S. Pat. Nos. 4,783,607 and 4,820,937 issued to Hsieh. His voltage source has a large voltage oscillation of power supply. Furthermore, this voltage oscillation of power supply has the impact on the input reference signal, 1.4 volts. He has to adopt the Schmitt trigger type input buffer to reject the noise caused by TTL power supply. My buffer can serve as the TTL power supply without the noise of power supply. The output load doesn't impact on the input reference signal, either. It is the best TTL power supply for the TTL compatible input buffer.